Urinary Tract Infection Symptoms in Children: From Infancy to School Age

A urinary tract infection in a child can occur at two levels: cystitis, which affects only the bladder, and pyelonephritis, which reaches the kidney. In practice, fever is what distinguishes the two: an infection with a fever of 38 °C or higher is considered to involve the kidney until proven otherwise. This distinction matters because cystitis is uncomfortable but does not harm the kidney, whereas in a kidney infection, delayed treatment can leave a permanent mark — a scar.

During the diaper years, the picture is silent and is often mistaken for another illness. In an infant, the following findings raise suspicion of a urinary tract infection:

• Fever with no identifiable cause — the only symptom in many infants
• Fussiness, inconsolability, or, conversely, excessive sleepiness
• Poor feeding, loss of appetite, vomiting, diarrhea
• Poor weight gain, falling off the growth curve
• Prolonged jaundice in a newborn
• Foul-smelling or cloudy urine; an odor that becomes noticeable at diaper changes
• Crying and fussiness while urinating
• Rarely, a drop in body temperature instead of fever

• None of these findings is diagnostic on its own — all of them can have many causes, from an upper respiratory infection to teething. What sets a UTI apart is that the fever cannot be explained by another source. In an infant under three months, a fever of 38 °C or higher calls for same-day evaluation regardless of any apparent source.

As toilet training progresses, symptoms come to resemble those in adults, and the child becomes able to show what is bothering them:

• Burning, stinging, or pain while urinating
• Frequent urination, sudden urgency, not making it to the toilet in time
• New wetting at night or daytime leaking in a child who was previously dry
• Lower abdominal pain; flank or back pain if the kidney is involved
• Fever, chills, fatigue, loss of appetite
• Cloudy, foul-smelling, or bloody urine
• Nausea and vomiting

Urinary tract infection is more common in male infants during the first year of life, and more common in girls afterward. In girls, the short urethra makes it easier for bacteria to reach the bladder, which is why most infections after the toilet-training period occur in girls. Constipation, holding urine for long periods, and wiping back-to-front increase this risk.

Starting treatment within the first 48 hours when a febrile urinary tract infection is suspected has been reported to reduce the risk of scarring in the kidney; a urine sample should therefore be collected rather than waiting. Seek same-day care, going to the emergency department if necessary, in the following situations:

• Fever of 38 °C or higher in an infant under 3 months
• Persistent vomiting, inability to take fluids, or a marked drop in urine output together with fever
• An infant who is excessively sleepy, hard to wake, or cannot be consoled
• Chills, pale or mottled-looking skin, rapid breathing
• Severe flank pain, back pain, or abdominal tenderness
• Fever persisting, or overall condition worsening, 48–72 hours after starting antibiotics
• Fever developing in a child with known kidney reflux, a single kidney, catheter use, or while on antibiotic prophylaxis

Symptoms raise suspicion; the diagnosis is made by urinalysis and urine culture. What is looked for is both the presence of inflammatory cells on urinalysis and the growth of a single bacterium in significant numbers on culture. For this reason, foul-smelling urine or frequent trips to the toilet, on their own, are not enough to start antibiotics.

Infection usually begins when bacteria from the bowel (most often E. coli) travel up the urethra into the bladder. A bladder that empties regularly and completely clears these bacteria out; problems arise when emptying is impaired or when urine flows backward into the kidney. The main contributing factors are:

• Constipation: a full bowel presses on the bladder and prevents complete emptying; most families do not realize their child is constipated
• Holding urine and infrequent voiding: avoiding the toilet at school is the most common example
• Bladder-bowel dysfunction (BBD): a combination of urgency, leaking, incomplete emptying, and constipation
• Low fluid intake
• Kidney reflux: backflow of urine from the bladder up the ureter into the kidney
• Structural causes: posterior urethral valves, duplex collecting system, ureterocele, ureteral obstruction, stones, neurogenic bladder
• Being uncircumcised in male infants; hygiene habits such as not wiping front-to-back in girls

• Urinary tract infection is not a disease that spreads from person to person; it is not passed on through pools, shared toilets, or contact. If infection recurs, one of the underlying factors above is looked for.

Kidney reflux is found in roughly 25–40% of children who have had a febrile urinary tract infection, so the first febrile infection is often the first sign of reflux. That said, not every child who has an infection undergoes a voiding cystourethrogram. VCUG (voiding cystourethrogram), the study that demonstrates and grades reflux, is recommended by guidelines for selected children rather than everyone; the main criteria are:

• Infants under 2 years old, especially under 6 months
• Recurrent febrile infection
• A severe or unusual course: no response to treatment within 48 hours, or a bacterium other than E. coli
• Kidney or ureteral dilation on ultrasound, suspected scarring, or another anomaly
• A family history of kidney reflux (mother, father, or sibling)
• Male infant